Not sure how SD 4.x series worked, but here's the way I'd work it. 1) A custom date field of "2nd Lvl Start" is populated automatically (or by rule) once a 2nd level group assigns the ticket to an individual. 2) Actual Finish is populated manually (or by rule) as the status moves to Completed (or your equivalent).
Then you just need a Crystal report or something to measure the time differences for you.
Not sure how this will survive migrations. Given our experience with the 5.x series, I'd say they won't. Plus with ServiceCenter coming out, I'll bet cash money NOTHING will migrate.